The invention is based on a method of detecting a target by means of an HPRF radar system.
The invention particularly relates to the detection of fast-moving targets, such as aircraft, by means of a pulse-Doppler radar system. Here a sequence (burst) of generally modulated pulses is emitted by a transmitter/receiver antenna. These pulses are reflected at a target to be detected, for example an aircraft, and received by the transmitter/receiver antenna. The evaluation of the measured transit time, or Doppler shift, of the pulses permits a determination of the velocity and the range of the target. Interfering ambiguities can occur in a manner known per se, particularly in the determination of the target range. Specifically, an unambiguous distance range exists for each predeterminable Pulse-Repetition Frequency (PRF). The higher the PRF is selected to be, the smaller the unambiguous distance range. On the other hand, even with fast-moving targets, such as fast aircraft, a high PRF (HPRF, "High Pulse Repetition Frequency") is required for attaining the highest-possible unambiguous velocity range. If there should be a large, expanded unambiguous distance range having a predeterminable, high unambiguous speed range, it is obvious to use an HPRF radar system having at least two switchable PRFs. In this case, generally a change in the PRF occurs with each emission of a burst, that is, switching generally occurs cyclically between the used PRFs. The received echo pulses associated with each PRF are then evaluated and compared to those of other PRFs. With the assumption that a target is impacted by the pulses of numerous different PRFS, both the target velocity and its range can be determined in the expanded unambiguous distance range.